The present invention relates to an electric machine comprising a first active part, a second active part which interacts with the first active part, and a sensor device for determining a kinematic quantity between the first and the second active part.
As a rule, operating a synchronous servomotor as inverter requires a position signal for determining the instantaneous commutation angle and/or for position control. This signal is usually obtained by an external position measuring system which is independent of the active parts of the motor. For this purpose, magnetic material measures with corresponding magnetic sensing principles are used more and more frequently instead of optical ones for cost reasons and because of their robustness against soiling. For speed acquisition, tachogenerators can be used in principle, but they only play a subordinate role particularly in the case of direct drives. For the acquisition of relative acceleration, in contrast, Ferraris sensors measuring on the basis of the eddy current principle are very suitable, the material measure of which consists of a non-magnetic metal strip, mostly of aluminum.
The said sensors are more or less sensitive to magnetic leakage fields which, however, are inevitably radiated by the electric machines. Particularly in the case of direct drives (linear and torque motors), measuring errors or even the destruction of the sensor occur if the leakage-field-sensitive sensors are correspondingly close to the active parts of the motor.
With regard to these problems, it has therefore been pointed out hitherto in the case of the magnetic position measuring systems that a certain distance from strong magnets must be kept.
However, this is opposed to a construction which is as compact as possible and to an integration of such a sensor directly in or at the motor components which is frequently advantageous also for control related reasons.